Create a base class for DateTimeFieldTest and DateRangeFieldTest and move common code into it

We may want to merge this with #2780063: Convert web tests to browser tests for datetime and datetime_range modules and do both at the same time. This may depend on how some of the new traits on BTB go. There are still a bunch missing to make this an easy conversion.

Regarding #2, I recommend not blocking things on a BTB conversion. See my feedback on the BTB meta for why we can't convert individual module tests to BTB at this time: #2735005-69: Convert all Simpletest web tests to BrowserTestBase (or UnitTestBase/KernelTestBase)

Patch (not converted to BTB).

Forgot the @group in base class.

This is looking really great! Thanks @claudiu.cristea!

I'm not clear on if this can go into 8.2 or not, but we'll leave it there for now.

A couple of small changes and it is looking good.

1. +++ b/core/modules/datetime/src/Tests/DateTestBase.php
   @@ -0,0 +1,181 @@
   +      // A timezone with an offset greater than UTC+12 is used.
   

   While we're refactoring this, let's remove this incorrect comment (this goes back to when the timezone loop was added, but the comment was never cleaned up).

2. +++ b/core/modules/datetime_range/src/Tests/DateRangeFieldTest.php
   @@ -88,56 +37,17 @@ class DateRangeFieldTest extends WebTestBase {
   +    $this->dateFormatter = $this->container->get('date.formatter');
   

   Can we add this property to the base class instead, and have the datetime field test use that as well? (It currently uses \Drupal::service('date.formatter').)

Thank you @jhedstrom

Here are the changes.

This looks great, thanks @claudiu.cristea!

I am still uncertain which branch it can go into.

Bumping up to 8.3.x, as it will need to go in there before it goes into 8.2.x (if it can).

Nice cleanup! Committed f03979c and pushed to 8.3.x and 8.2.x. Thanks!

Fixed the following coding standards violation on commit:

FILE: .../git/maintainer/core/modules/datetime/src/Tests/DateTestBase.php
----------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
----------------------------------------------------------------------
 111 | ERROR | [x] Expected 1 space after "="; 2 found
----------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
----------------------------------------------------------------------

diff --git a/core/modules/datetime/src/Tests/DateTestBase.php b/core/modules/datetime/src/Tests/DateTestBase.php
index 4c9d01c..0f1277e 100644
--- a/core/modules/datetime/src/Tests/DateTestBase.php
+++ b/core/modules/datetime/src/Tests/DateTestBase.php
@@ -108,7 +108,7 @@ protected function setUp() {
   protected function createField() {
     $field_name = Unicode::strtolower($this->randomMachineName());
     $type = $this->getTestFieldType();
-    $widget_type = $formatter_type =  $type . '_default';
+    $widget_type = $formatter_type = $type . '_default';
 
     $this->fieldStorage = FieldStorageConfig::create([
       'field_name' => $field_name,

Back to fixed :)